Field of the Invention
Embodiments of the invention generally relate to a cross-sensitivity-compensated biosensor.
Description of the Related Art
Hereinafter, a sensor used for the detection or concentration determination of analytes in media inside or outside a human or animal body will be referred to as a biosensor. In addition, hereinafter, a medium that potentially contains an analyte which is to be detected or of which the concentration is to be determined will be referred to as a test medium.
Generally, in order to provide new sensors for the concentration determination or the detection of substances, polymer networks may be used. Polymer networks are polymers of which the molecules are chemically linked (for example by covalent or ionic bonds) or physically linked (for example by entanglement of the polymer chains) to form a three-dimensional network. A network of this type swells in the presence of an opportune solvent by absorbing the solvent. Typically, the swollen network is then also referred to as a gel or polymer gel. If water is the swelling agent, reference is also made to a hydrogel. As special gels, “smart” gels (“smart” hydrogels when water is used as swelling agent) have the ability under certain preconditions to selectively respond to changes in ambient variables, this response being manifested by changes in volume. Sensitivities may be attained in particular with respect to temperature, pH value, ion concentration, or substance concentration. Such polymer networks may thus respond by means of a significant volume change as a result of water uptake or water release in the event of a change to the concentration of a substance, for example in the blood. Introduced into a defined volume, the concentration-dependent volume change may be converted into a concentration-dependent pressure change. This is relevant in particular in the case of sensors by means of which the concentration of certain substances (for example what are known as biomarkers, for example in the blood) may be determined.
For the production of “smart” gels, base materials are often used that, besides being dependent on the sensitivities to the substances for detection or concentration determination of which said materials have been produced, additionally are heavily dependent on other ion or substance concentrations and/or temperature and/or pH value, i.e. these gels may change their solvent content (or volume) depending on ion or substance concentrations and/or depending on temperature and/or pH value. The volume change or pressure change of the gel are thus dependent on the concentration of the substance, i.e. the actual sensor measurand, and the concentration of other ion and/or substance concentrations and/or the temperature and/or pH value. It has been found that the volume change or swelling pressure change in the event of variations in temperature and/or pH value are much greater than those volume or swelling pressure changes caused by a change to the actual sensor measurand, for example the concentration of the blood component when using “smart” hydrogels.
The sensitivity of a sensor to variables other than the variable to be measured is referred to as cross-sensitivity. The variable to be measured is the measurand or also sensor measurand. A variable that is not the measurand, however, influences the information delivered by the measuring device concerning the measured value, i.e. is an influencing variable. The influencing variable means that the measured value changes merely as a result of a change to the influencing variable.
United States Patent Publication 2010/0056888 A1, to Skerl et al., entitled “Implantable Biosensor and Sensor Arrangement”, discloses an implantable biosensor, in which a hydrogel may be used for the detection of an analyte. As disclosed in Skerl et al., a hydrogel may undergo a significant volume change in the presence of a suitable analyte. According to Skerl et al., pressure sensors are used in order to measure a concentration of an analyte. One measures the pressure in a measurement chamber, which pressure may vary by the analyte, whereas another measures the pressure outside the measurement chamber. In Skerl et al., the content of the analyte in the measurement chamber is determined from the pressure difference. The two pressure values may also be used for temperature compensation.
For example, United States Patent Publication 2009/0275815 A1, to Bickoff et al., entitled “Temperature-Compensated In-Vivo Sensor”, discloses a system comprising a biosensor for measuring the concentration of an analyte and a temperature sensor, which detects the temperature in a region as close to the biosensor as possible. In Bickoff et al., the output signal of the biosensor is corrected with the measured temperature in order to determine the measured analyte concentration.
The high technical demands on the sensor system, such as measurement ranges and resolution of the pressure and temperature sensor, may be satisfied only with difficulty for the highly precise detection of medically relevant concentration changes in the blood, in particular in a transportable or implantable system.